7 Photochromism
277
1 mm
UV
UV
S
S
F
F
F
F
F
F
Me
Me
F
F
F
F
F
F
F
F
S
S
F
F
F
F
F
F
Me
Me
F
F
F
F
F
F
F
F
UV
Vis.
Fig. 7.17 Photomechanical work of molecular crystal cranes composed on a diarylethene and
perfluoronaphthalene. UV light was irradiated from the lower side of the crystal: 2-mm lead ball,
46.77 mg; crystal, 0.17 mg. Adapted from Morimoto and Irie (2010) with permission from American
Chemical Society
with a length of 1−5 mm exhibited photoreversible bending behavior over 250 times
(Morimoto and Irie 2010). The crystals were able to lift a heavy metal that was 200
times heavier than the crystals, like “molecular crystal cranes”, as shown in Fig. 7.17.
The photogenerated maximum stress in the crystals was estimated to be 44 MPa,
which is 100 times larger than that of muscle (ca. 0.3 MPa). Young’s modulus of the
crystal was measured to be 11 GPa. The relatively large Young’s modulus enabled
the crystals to perform large mechanical work.
Mixed crystals composed of two diarylethenes also exhibited more than 1000
reversible bending cycles upon alternating irradiation with UV and visible light
without any crystal destruction (Terao et al. 2012). The crystal exhibited a bending
motion across a wide temperature range from 4.6–370 K and even in water. The
rod-like crystal bent toward the incident light source irrespective of the irradiation
direction. The edge of the rod-like crystal could be rotated when the light intensity of
the UV and visible lights was controlled, which resulted in actual mechanical work
to rotate a gearwheel.
The bending behavior of a gold-coated diarylethene crystal was investigated (Kitagawa and Kobatake 2015). The photoreversible current ON/OFF switching of an
electric circuit by the gold-coated diarylethene crystal was demonstrated as shown
in Fig. 7.18. The current was able to flow in a stable manner even when the current
value was over 0.5 mA. The current switching could be repeated over 10 cycles.
Thus, gold-coated diarylethene crystals could be used as real photoactuator in the
mesoscopic region.
277
1 mm
UV
UV
S
S
F
F
F
F
F
F
Me
Me
F
F
F
F
F
F
F
F
S
S
F
F
F
F
F
F
Me
Me
F
F
F
F
F
F
F
F
UV
Vis.
Fig. 7.17 Photomechanical work of molecular crystal cranes composed on a diarylethene and
perfluoronaphthalene. UV light was irradiated from the lower side of the crystal: 2-mm lead ball,
46.77 mg; crystal, 0.17 mg. Adapted from Morimoto and Irie (2010) with permission from American
Chemical Society
with a length of 1−5 mm exhibited photoreversible bending behavior over 250 times
(Morimoto and Irie 2010). The crystals were able to lift a heavy metal that was 200
times heavier than the crystals, like “molecular crystal cranes”, as shown in Fig. 7.17.
The photogenerated maximum stress in the crystals was estimated to be 44 MPa,
which is 100 times larger than that of muscle (ca. 0.3 MPa). Young’s modulus of the
crystal was measured to be 11 GPa. The relatively large Young’s modulus enabled
the crystals to perform large mechanical work.
Mixed crystals composed of two diarylethenes also exhibited more than 1000
reversible bending cycles upon alternating irradiation with UV and visible light
without any crystal destruction (Terao et al. 2012). The crystal exhibited a bending
motion across a wide temperature range from 4.6–370 K and even in water. The
rod-like crystal bent toward the incident light source irrespective of the irradiation
direction. The edge of the rod-like crystal could be rotated when the light intensity of
the UV and visible lights was controlled, which resulted in actual mechanical work
to rotate a gearwheel.
The bending behavior of a gold-coated diarylethene crystal was investigated (Kitagawa and Kobatake 2015). The photoreversible current ON/OFF switching of an
electric circuit by the gold-coated diarylethene crystal was demonstrated as shown
in Fig. 7.18. The current was able to flow in a stable manner even when the current
value was over 0.5 mA. The current switching could be repeated over 10 cycles.
Thus, gold-coated diarylethene crystals could be used as real photoactuator in the
mesoscopic region.